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The year 2005 has been named the World Year of
Physics in recognition of the 100th anniversary of Albert
Einstein's "Miracle
Year," in which he published four landmark papers, and the
subsequent advances in the field of physics.

The mass–energy equivalence formula was displayed on Taipei 101 during the
event of the World Year of Physics
2005.

History

Physics has been the
basis for understanding the physical world and nature as a whole.
The applications of physics are the basis for much of today's
technology. In order to both raise the worldwide awareness of
physics and celebrate the major advances made in the field, the International Union
of Pure and Applied Physics resolved that 2005 should be
commemorated as the World Year of Physics. This has subsequently
been endorsed by both the United Nations and the United States Congress[1].

Most physicists agree that the first three of those papers
deserved Nobel
Prizes, but only the paper on the photoelectric effect would
win one. What makes these papers remarkable is that, in each case,
Einstein boldly took an idea from theoretical physics to its
logical consequences and managed to explain experimental results
that had baffled scientists for decades.

Photoelectric effect

The first paper proposed the idea of "energy quanta" and showed how it could be used
to explain such phenomena as the photoelectric effect. The idea of
energy quanta was motivated by Max Planck's earlier derivation of the law
of black-body radiation by assuming that luminous energy
could only be absorbed or emitted in discrete amounts, called
quanta. Einstein showed that, by assuming that light actually consisted
of discrete packets, he could explain the mysterious photoelectric
effect.

The idea of light quanta contradicted the wave theory of light
that followed naturally from James Clerk Maxwell's equations for electromagnetic behavior and, more
generally, the assumption of infinite divisibility of energy
in physical systems. Even after experiments showed that Einstein's
equations for the photoelectric effect were accurate, his
explanation was not universally accepted. However, by 1921, when he
was awarded the Nobel Prize and his work on photoelectricity was
mentioned by name in the award citation, most physicists thought
that light quanta were possible. A complete picture of the
photoelectric effect was only obtained after the maturity of
quantum mechanics.

Brownian
motion

His second article that year delineated a stochastic model of Brownian
motion. Brownian motion generates expressions for the root mean
squaredisplacement of particles. Using
the then-controversial kinetic theory of fluids, it established
that the phenomenon, which still lacked a satisfactory explanation
decades after it was first observed, provided empirical evidence
for the reality of atoms. It also
lent credence to statistical mechanics, which was
also controversial at the time.

Before this paper, atoms were recognized as a useful concept,
but physicists and chemists hotly debated whether atoms were real
entities. Einstein's statistical discussion of atomic behavior gave
experimentalists a way to count atoms by looking through an
ordinary microscope. Wilhelm Ostwald, one of the leaders of
the anti-atom school, later told Arnold Sommerfeld that he had been
converted to a belief in atoms by Einstein's complete explanation
of Brownian motion.

Special
relativity

Einstein's third paper that year was a highly self-contained
work, hardly making reference to other works which may have led to
its development. This paper introduced a theory of time, distance,
mass and energy which was consistent with electromagnetism, but omitted the
force of gravity.

Special relativity avoids the problem in science that was
present after the Michelson-Morley experiment failed to
measure a speed difference between perpendicular light beams, by
postulating that the speed of light is not relative
to some medium and is the same for all observers irrespective of
their relative velocities. This is unlike all other known waves, which require a medium (such
as water or air) to propagate.

Einstein's explanation arises from two postulates: The first is
Galileo's
idea that the laws of nature are the same for all
observers that move with constant velocity relative to each other.
The second was that the speed of light is the same for every
observer.

Special relativity has several striking consequences, because
the concepts of absolute time and space are incompatible with an
absolute speed of light. The theory abounds with paradoxes and appeared to make little sense,
landing Einstein substantial ridicule, but he eventually managed to
work out the apparent contradictions and solve the problems.

Consequences

Einstein's special theory of relativity heralded a new kind of
physics, one that digressed from the classical mechanics that had
been derived from Newton's calculus. Although his 1905 paper on the
photoelectric effect helped spur the development of quantum
mechanics, Einstein himself considered quantum theory, which
introduced the concept of uncertainty into the laws of the
physical world, incomplete. His deterministic view is illustrated
in the famous quote "I am convinced that He (God) does not play dice." Einstein viewed quantum
mechanics as a means simply to the end of a unified
field theory, which would unite the disparate theories of quantum
field theory, general relativity, and electromagnetism. However, he never
denied that quantum mechanics was very successful in explaining and
predicting physical phenomena.

In Berlin, sixteen large,
red E's have been erected along a section of the famous Unter den
Linden boulevard. Called the "Einstein Mile", the E's,
which has been in place from April to September 2005 displaying
information on the theories and life of Albert Einstein.